1. Field
This disclosure relates generally to memories, and more specifically, to memories having electrically programmable fuses.
2. Related Art
Fuses have been used successfully for many years in implementing a variety of functions that require programming just once. One example is implementing redundancy in a memory. Another example is for providing information about the particular integrated circuit such as lot number and when manufactured. Another use is at a point of sale programming for a particular user such as for a purchaser of a mobile phone or a change in service provider. Fuse programming is one type of the general category known as one time programmable (OTP) memories. An OTP memory may use floating gate technology. A disadvantage of floating gate memories is that they require significant special processing from that required for single gate transistors that are used for logic, buffering, and other uses. Fuses generally require significantly more space than floating gate memories so are commonly used when the amount of memory that is required is relatively small, such as for the uses described above. Laser programmable fuses of course require a laser and the extra processing required for the laser programming function. Additionally the fuse has to be in a position where it can be blown by an overhead laser. One issue with electrically programmable fuses is that they require significant current in order to be programmed. Thus there are transistors that must be of sufficient size to handle these relatively high currents. Further, the voltages applied to the transistors, in order to pass these high currents, generally need to be higher than the power supply voltage used to power the logic transistors. Also, electrically programmable fuses that are on the same word line or bit line as the one being programmed are susceptible to having their logic state changed. This is sometimes called write disturb, which is a known problem but which also can be a difficult problem to overcome.
Thus, there is a need for a method for programming electrically programmable fuses that improve on the issues described above.